Rectifier sealing



mg., m, wm.

P. E. FREEMAN RECTIFIER SEALING Filed March 4, 1937 Patented Aug. 1e, 193s.

asoma SEALING Paul B. Freemanrlndianapolis, Ind., assigner to. l P. B. Mallory ds Co., Inc, Indianapolis, Ind., a. corporation. of Delaware Application March 4, 1931, serial No.' 128.953 Y s claims. (ci. ris-aes) a This invention relates to dry disc rectiners.

An object 'of the invention is to improve a rectifler of the dry disc-type.

Another object is to improve the sealing means 5 for a dry disc rectier.

Other objects of the invention will be apparent from. the following ldescription vand accompanying drawing taken in connection with the ap- Beaded claims.

V:lil The invention comprises the features of construction, combination of elements, arrangement yof parts. and methods of manufacture and operation referred to above or which will be brought vout and exemplified inthe disclosure hereinafter ins.

In the drawing: Figure 1 is a longitudinal section `through a dry disc rectier embodying features of the present invention; Figure 2 is an end view of the rectifier with parts broken away; and

Figure 3 shows a modified form of bolt for the rectifier. In its preferred form the present invention involves a novel sealing means for a drydisc rectiflergwhereby its performance is materially iinproved. v

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the meth- -od of procedure andthefconstruction of parts without departingfrom the spirit of the invention. In the following description and in the 16 set forth, including the illustrations in the draw-- '35 claims, parts will be identied by specific names 40 ble to rectiilers of the type set forth in Samuel Ruben Patents 1,751,359.' v1,751,361 and 1,751,363 issued March 18, 1930 and others. One commercial form of the rectifier comprises ,copper sulfide washers each having one face in contact with a magnesium washer andthe opposite face in contact with a non-polarizing layer such as a washer .or carbonized nickel. The washers are arranged in face to face contactin proper sequence with larger radiating fins at suitable intervals and a bolt passing'through the center for clamping the .groups of discs together.-

Heretofore such rectifl'ers have been sealed externally against the effects of moisture by coating the outer edges of the-washers with some 56 sort of protecting varnish or by some other exmoisture.

ternal sealing means and the ends ofthe assembly have been provided with a cork or rubber washer or gasket to prevent moisture from entering the internal space surrounding the clamping bolt. The sole purpose of such sealing has 5 been to protect the junctions from the deleterious effects of moisture.

I have now discovered that the performance of the rectifier can be materially improved by sealing both the inside and the outside edges of 10 the rectifier elements with a suitablesealing means, such as insulating varnish.

This improvement in performance extends far beyond a mere improvement in sealing against The sealing I propose appears to. ma- 16 terially affect the electric breakdown character-A istics of the rectier.

- The improvement in current rectifying capac- Vity is remarkable. It has been found, for example. that a rectifier junction 1%" in diameter, 20

protected by insulating varnish on both the in- J'ner and the outer edges of therectier discs will safely deliver amperes D. C. when connected` in a 3-phase bridge rectifier. The same junction sealed in the conventional manner by cork wash- 25 ers at the end of the rectifier so as to adequately exclude moisture is unable, onthe other hand, to deliver more than approximately 30 to 50 amperes without such serious sparking across the junction as would cause complete breakdown of- 3d ythe rectifier in a relatively few-hours of operation.

While Ido not wish to belimited to any particular theory of operation it is my lpresent opinion that the following theory might explain the 35 phenomenon: In making the copper sulde rectier the magnesium disc is pressed firmly against the cupric sulde disc and an intermediate film is formed by the passage of electric current through a dielectric film previously created' on 40 the magnesium by a chemical process. The electric forming process is continued until al1 of the magnesium area in sufficiently close contact with in voltage across the Junction due to the passage of high currents or a.\combination of these two `causes probably results in ionization of the air in this very narrow gap, which in turn produces an arc. The' destructive or erosive eect of this are with high currents will cause the point of actual contact between. discs to move inwardly According to the present invention, the narrow gap between the edges of the discs is illled with a dielectric material which excludes air from the gap whereby no ionization can take place and there can be no arc created from this cause.

The drawing illustrates a rectifier sealed in the preferred manner of the present invention. Each cupric sulnde washer .l is in contact on one face with a magnesium washer Il between lwhich a suitable rectifying layerv is formed by passage of an/electric current as mentioned above. -The otherface of the copper sulfide washer I0 is in contact with a non-polarizing layer I2, such as a carbonized nickel disc or one of pure-iron, or nickel plated steel, and the like. Two groups of these rectifying units are interposed between each pair of radiating plates i3' which may be of any suitable metal, such as steel.

In the present instance the rectifier is intended for full wave operation and accordingly five spaced radiating plates I3 are used providing four rectifier sections. 'I'hese sections can be connected in the fourarms of the bridge by four terminals I4, l5, I6 and i1., The rectier' plates in each section are arranged in such polarity as to provide DC across terminals I and I1 when AC is imposed across terminals I4 and I6.

The rectifier assembly is held together by bolt I8 passing through the holes in the center of the rectifier disc members. A pair of end washers 22, 24 and 23, 25 are included at each end of the assembly. Washers 22 and 23 are disposed directly on top of the end plates and are slotted to permit introduction of the insulating varnish. The assembly is held under compression by spring washer 20 which is tightened against the end of the assembly by nut I9 on bolt I8. l

According to the invention a sealing varnish 26 is coated over the internal and external edges of the rectifier washers. 'I'he .varnish used should preferably have a low surface tension when ap' plied so as to flow into the narrow spaces at the edge of the discs and completely exclude air from contact with the disc edges. Air pockets should be carefully avoided. The varnish should also preferably have a Vhigh dielectric strength. One varnish which has been found very satisfactory is made according to the following procedure: 100 pounds Robertson's wax, 12 gallons of raw tung oil and 5 pounds manganese resinate are cooked.

together at approximately 250 C. until the mixture is ready to yJell and then allowed to cool. While it is cooling 31 gallons of petroleum naptha are added as rapidly as possible to complete the varnish.

The varnish may be applied to the clamped assembly before the end washers and nut are put on but preferably may be introduced through' the material at the edge of the gap or an increase slots or'aperturesl 2| in the end washers. The assembly may then be baked to solidify and harden the varnish.

In Figure 3 is shown a modified form of bolt 21 having a hollow core 28 and a pair of radial openings 28 and 30 in the wall thereof. When this bolt is -used in place of bolt I8 the slotted washers are not required as the varnish 26 may be introduced through the hollow core. and radial openings. This form of bolt is particularly applicable to the larger sizes of rectiiiers.

While the present invention, as to its lobjects and advantages has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. A dry disc rectifier comprising a plurality of rectifier discs in face-to-face contact said discshaving inner and outer edges and an insulating sealing material in solid adherent formcovering all the edges of saiddiscs so as to exclude air from the .edge surfacesy of said discs. A 2. A dry disc rectifier comprising a'series of rectifier discs having central apertures therein, said discs being in face-to-face contact withthe central apertures of all said discs in, register, and a solid adherent insulating sealing material coat- ,ing the inner and outer edges of said discs.

3. A dry disc rectifier comprising a series'l of rectifier discs having central apertures therein said discs being in face-to-fa ce contact with the rectifier discs having central 'apertures therein said'discs being in face-to-face contact with the central apertures of all said discs in register, and a'n insulating varnish coating the inner and outer edges of said discs.

5. A dry disc rectifier comprising a series of rectifier discs having central apertures therein and discs being in face-to-face contact with the central apertures of all said discs in register, and an insulating varnish coating the inner and outer edges of said discs so as to seal all the edge surfaces thereof.

6. A dry disc rectifier comprising a pair of rectifier discs having central apertures therein', said discs being in face-to-face contact with the central apertures of said discs in register,'said discs thereby providing a rectifying junction between them, and a solid adherent insulating sealing material covering the inner and outer edges of the junction of said discs so as to excludeair from the edge surfaces of said junction.

7. A dry disc rectifier comprising a. pair ofrec- 1 tier discs having central apertures therein, said disc being in face-to-face contact with the central apertures of said discs in register, said discs lthereby providing a ,rectifying junction between them, and a solid adherent insulating varnish covering the inner and outer edges of the junction of said discs so as to ,excludeair from the edge surfaces of said junction.,

8. A dry plate rectifier comprising a Aser-ies of rectifier plates having an aperture therethrough, said plates being in face-to-fac contact anda solid adherent sealing material coating the inner and outer edges of said plates.

PAUL B. FREEMAN'. 

